Colonography on an unprepared colon

ABSTRACT

A method for generating colonography images for colorectal screening of a patient. The patient is administered an amount of radiopaque stool marker which will enable stool present in the patient&#39;s colon to be distinguished from soft tissue. The patient&#39;s colon is imaged after the stool marker has been administered to generate colonography images. Preparation of the colon is simulated by processing the colonography images to remove marked stool before the images are observed during a diagnosis session.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/253,673,filed on Sep. 24, 2002 now U.S. Pat. No. 7,035,681, and entitled“COLONOGRAPHY OF AN UNPREPARED COLON,” which is a continuation ofapplication Ser. No. 09/522,389, filed on Mar. 10, 2000, and entitled“COLONOGRAPHY OF AN UNPREPARED COLON,” now U.S. Pat. No. 6,477,401,issued Nov. 5, 2002, which are incorporated herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally colonography (also known ascomputed tomographic colonography or CTC), a minimally invasive imagingtechnique for colorectal cancer screening. In particular, the inventionis a method for generating colonography images that does not requirecathartic preparation of the colon prior to the imaging.

BACKGROUND OF THE INVENTION

Colonography, the use of electronic imaging technologies such ascomputed tomography (CT) to generate images of a patient's colon forpurposes of colorectal cancer screening, is generally known.Descriptions of this diagnostic methodology can, for example, be foundin the Johnson et al. U.S. Pat. No. 5,891,030, the Johnson et al. PCTpublication WO 98/32371, the Vining U.S. Pat. No. 5,782,762 and theVining et al. U.S. Pat. No. 5,920,319, all of which are herebyincorporated by reference. Briefly, this methodology involves obtaininga series of CT images of adjacent portions or slices of the colon. Aradiologist then studies each of the images to identify anypre-cancerous polyps. Also known as virtual colonoscopy, this techniqueeffectively creates a computer simulated intraluminal flight through thecolon. This dynamic diagnostic methodology has been demonstrated to be ahighly efficacious approach for detecting colorectal polyps.

Although these known colonography approaches are generally much lessinvasive and more comfortable for the patient that other colorectalcancer screening techniques such a colonoscopy, they still require thatthe patient's colon be prepared (i.e., cleansed of stool) through theuse of laxatives or other cathartics. Removal of the stool is requiredbecause the stool exhibits the same density to the imaging processes asthe polyps and soft colon tissue. In other words, the stool looks verysimilar to polyps and the tissues of the colon in the colonographyimages. The presence of stool can therefore mask polyps and otherfeatures in the images that may be relevant to the diagnostic process.Unfortunately, these colon preparation processes can be time consumingand uncomfortable for the patient. Patient compliance with thepreparation processes is sometimes therefore poor, resulting in reducedefficacy of the diagnostic procedure. Perhaps even worse, some patientsmay forego the diagnostic procedure altogether to avoid theinconvenience of the preparation process.

It is evident that there is a continuing need for improved colonographymethodologies. In particular, there is a need for colonographymethodologies that are less sensitive to the need for thorough colonpreparation prior to imaging. A methodology that does not requiresubstantial preparation would be particularly desirable. To be viable,any such method must be highly efficacious and efficient to perform. Acolonography approach which meets these objectives could enhance patientacceptance of the diagnostic procedure and reduce the morbidity ofcolorectal cancer.

SUMMARY OF THE INVENTION

The present invention is a highly efficacious and convenient method forgenerating colonography images for colorectal cancer screening. Oneembodiment of the invention includes administering to the patient anamount of stool marker which will enable stool present in the patient'scolon to be distinguished from soft tissue. The stool marker can beadministered in liquid or pill form. Following administration of thestool marker, the patient's colon is imaged to generate the colonographyimages. The colonography images are then processed to mark or remove themarked stool and simulate the preparation of the colon. The images canthen be displayed to a radiologist during a diagnosis session.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a computed tomographic (CT)workstation which can be used in connection with the colonography methodof the present invention.

FIG. 2 is a flowchart describing generally the colonography method ofthe present invention.

FIG. 3 is an image of a cross section of a patient's abdomen taken by aCT scanner.

FIG. 4 is a graph of the distribution of the pixel intensity values (onthe Houndsfield scale) of the image shown in FIG. 3.

FIG. 5 is a flowchart describing the marked stool identification stepshown in FIG. 2.

FIG. 6 is a detailed image of a portion of the colon shown in FIG. 3.

FIG. 7 is a graph of the pixel intensity values (not to scale) of aportion of one of the rows of pixels of the image shown in FIG. 6.

FIG. 8 is an image of the portion of the colon shown in FIG. 6 followingthe removal of the island of unmarked stool.

FIG. 9 is a flowchart describing the marked stool perimeter expansionstep shown in FIG. 5.

FIG. 10 is an image of the portion of the colon shown in FIG. 6following the removal of the identified stool.

FIG. 11 is an image of the portion of the colon shown in FIG. 6 showingthe stool as it would appear if not marked in accordance with thepresent invention.

FIG. 12 is a chart describing generally the barium sulfateadministration schedule or protocol during a test of the invention on agroup of patients.

FIG. 13 is a chart describing and illustrating in detail theadministration schedule for the groups of patients that received dosesof suspended barium sulfate over 24 hour periods.

FIG. 14 is a chart describing and illustrating in detail theadministration schedule for the groups of patients that received dosesof suspended barium sulfate over 48 hour periods.

FIG. 15 is an illustration of the scoring system used to quantify theamount of stool in the colons that was adequately marked by theassociated administration protocol during the test.

FIG. 16 is a CT image of a cross section of an abdomen includingportions of a colon, and a detailed CT image of a portion of the colon,illustrating an example of the type of marking that would be assigned ascore of 0 in the test.

FIG. 17 is a CT image of a cross section of an abdomen includingportions of a colon, and a detailed CT image of a portion of the colon,illustrating an example of the type of stool marking that would beassigned a score of 1 in the test.

FIG. 18 is a CT image of a cross section of an abdomen includingportions of a colon, and a detailed CT image of a portion of the colon,illustrating an example of the type of stool marking that would beassigned a score of 2 in the test.

FIG. 19 is a CT image of a cross section of an abdomen includingportions of a colon, and a detailed CT image of a portion of the colon,illustrating an example of the type of stool marking that would beassigned a score of 3 in the test.

FIG. 20 is a CT image of a cross section of an abdomen includingportions of a colon, and a detailed CT image of a portion of the colon,illustrating an example of the type of stool marking that would beassigned a score of 4 in the test.

FIG. 21 is a graph of the stool labeling efficacy obtained from the twogroups of patients administered doses of barium sulfate suspension overa 24 hour period in the test.

FIG. 22 is a graph of the stool labeling efficacy obtained from the twogroups of patients administered doses of barium sulfate suspension overa 48 hour period in the test.

FIG. 23 is a graph of the polyp detection results obtained from theimages generated during the test.

FIG. 24A is a two-dimensional CT image of portion of a colon whichincludes a section of stool marked in accordance with the presentinvention.

FIG. 24B is a two-dimensional CT image of the same portion of the colonshown in FIG. 24A, from which the section of marked stool has beenremoved in accordance with the present invention.

FIG. 25A is a three-dimensional CT image of portion of a colon whichincludes a section of stool marked in accordance with the presentinvention.

FIG. 25B is a three-dimensional CT image of the same portion of thecolon shown in FIG. 25A, from which the section of marked stool has beenremoved in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a method for performing colonography whichinvolves marking the stool present in the patient's colon with aradiopaque material before the colon is imaged. The marked stool canthen be electronically identified and effectively removed from theimages before the images are presented to a radiologist in a diagnosticsession. In effect, the method is capable of providing simulated colonpreparation and stool recognition. Highly efficacious colonographydiagnostic procedures can therefore be performed without subjecting thepatient to uncomfortable preparation processes.

FIG. 1 is an illustration of a computed tomographic (CT) imaging system8 which can be configured to implement the colonography methodology ofthe present invention. As shown, the system 8 includes a workstation 9having a computer 12 and user-actuated input/output devices such askeyboard 10 and mouse 16. Computer 12 includes a processor (notseparately shown), memory 18 and storage device 20 for reading andwriting data to removable storage media 22 such as compact disk readonly memory (CD ROM) or floppy disks. Programmed instructions (e.g.,software) for performing the image processing algorithms of theinvention described below, as well as other conventional aspects ofcolonography system, can be stored in the memory 18 and executed by theprocessor. Computer 12 can be coupled to other input/output devices (notshown) such as a local area network (LAN) or wide area network (WAN)through an interface cable (not shown). The system 8 also includes adisplay device such as monitor 14 which can be used to display thecolonography images 24 to a radiologist during a diagnostic session. Theradiologist can scroll through the images 24 and otherwise control thedisplay of the images through the use of keyboard 10 and/or mouse 16 inconnection with a graphical user interface (not shown) on monitor 14.System 8 is connected to an imaging instrument such as CT scanner 26through an external data bus 28. Prototypes of the invention have beendeveloped using images generated by a commercially available GeneralElectric Light Speed model CT scanner. However, other CT scanners, aswell as other imaging technologies such as electron beam tomography(EBT), magnetic resonance imaging (MRI), positron emission tomography(PET) and high resolution ultrasound can also be used in connection withthe invention.

FIG. 2 is a flow chart illustrating generally the colonography method 50of the present invention. As shown, the method 50 includes theadministration of a stool marker to the patient (step 52) followed bythe imaging of the patient's colon (step 54). The colonography imagesproduced during step 54 are then electronically processed to identifythe marked stool (step 56). The marked stool is preferablyelectronically removed from the colonography images (step 58), and theremoved stool replaced with an image representation of air or otherfeature (step 60). The processed colonography images are then displayedfor a diagnostic session by a radiologist (step 62).

The stool marker administered to the patient at step 52 is a compound orother substance which can be electronically identified in thecolonography images. In general, the stool marker will be opaque to thewavelength of radiation or other parameter (e.g., ultrasound) used bythe imaging instrument to generate the colonography images. Preferably,the stool marker has a density or other image-responsive characteristicwhich is sufficiently different than the density of stool and softtissues of the colon, and from air or other gas or substance within thecolon being imaged, to enhance the ability of the image processingalgorithm and/or a visual observer to efficiently and accuratelydistinguish the stool marked with the marker from the polyps and othertissues of the colon. Other desirable characteristics of the stoolmarker are its ability to completely mix with the stool presentthroughout the length of the colon being imaged, and its tendency to notcoat the colon wall. Thorough and homogeneous mixing with stoolthroughout the colon enhances the capability of the imaging processingalgorithm to maximize the identification of stool. The ability of theprocessing algorithm (or a radiologist visually observing the images) todistinguish between the marked stool and the colon tissues will beenhanced if the amount of marker on the colon walls is minimized. Asdescribed in greater detail below, orally consumed doses of liquidsuspended barium sulfate (which is radiopaque to CT imaging processes)administered over a period of twenty-four to forty-eight hoursimmediately prior to the colon imaging step 54 was used as a stoolmarker and associated protocol during tests of the invention.

Barium sulfate or other stool marker can also be administered in pillform. By way of example, the stool marker can be in tablet form, coatedtablet form or enclosed in a capsule. The pill form of the stool markercan be formulated to cause the effective release of the stool marker inthe stomach of the patient following its administration. Pill form stoolmarkers will enhance patient compliance with the administration of thestool marker by reducing any unpleasant taste of other effectsassociated with the consumption of the marker.

The colon imaging step 54 is performed in a conventional manner such asthose described in the patent documents identified in the Background ofthe Invention section. Preferably, the set of colonography imagesgenerated at step 54 are three dimensional (3D) images. Commerciallyavailable software programs such as VoxelView from Vital Images can beused for this purpose. Alternatively, efficacious colorectal screeningdiagnoses can be obtained through the use of two dimensional (2D)colonography images processed in accordance with the methodologydescribed herein.

FIG. 3 is an illustration of a CT colonography image of a cross sectionof a patient's abdomen 60. Visible in the image of abdomen 60 are thebones of the patients pelvis 62 and spine 64, as well as portions of thecolon 66. The images such as that shown in FIG. 3 which are viewed bythe radiologist are typically gray-scale images with the most densetissue (e.g., bone and marked stool) and other substances represented bythe lightest intensity shades (i.e., white) and the least dense tissueand other substances (e.g., air) represented by the darkest intensityshades (e.g., black). In this convention, the bones of pelvis 62 areshown as being white in the image, and the air within colon 66 shown asbeing black. The intensity of the individual pixels of the images arerepresented by digital pixel intensity values which can be processed bythe computer 12 (FIG. 1). CT images such as that shown in FIG. 3 usewhat is known as the Houndsfield scale to represent the range of pixelintensity values. On the Houndsfield scale a value of −1000 houndsfieldunits (HU) is used to represent the density of air and a value of 0 HUto represent water. Bone will generally have densities corresponding tobetween 500 and 1000 HU.

FIG. 4 is a graph of the number or distribution of the pixel intensityvalues in the image of abdomen 60 across the Houndsfield scale. Asshown, there is a concentration of pixel values around −1000 HU near thelower end of the scale, and a concentration of pixel values betweenapproximately −100 and 150 HU. The concentration of the pixel valuesaround −1000 HU generally represents the volume of air in the image(including that within the colon 66). The concentration of the pixelvalues centered at about −100 HU generally represents fat. Theconcentration of the pixel values centered at about 50 HU generallyrepresents muscle and other soft tissues such as unmarked stool andthose of the colon wall. Portions of the image represented by pixelintensity values greater than about 150 HU are generally bone or markedstool.

FIG. 6 is an illustration of a portion of a CT image of a colon 66having a wall 80 and a polyp 82 extending from the wall. A section ofmarked stool 84 is present within the colon 66 and surrounds the polyp82. Present within the marked stool 84 is a section of unmarked stool86. The air 88 within the colon 66 is the least dense and thereforedarkest portion of the image. The marked stool 84 is the most dense andtherefore lightest portion of the image. The tissues of the colon wall80 and the unmarked stool 86 have a density and therefore gray-scaleshade which is between those of the air 88 and marked stool 84.

FIG. 7 is a graph (not to scale) of the intensity values (in HU) of thepixels along the portion of row 90 in the image shown in FIG. 6. Asshown, the pixels of the row 90 include a group P which extends throughthe polyp 82, a group S which extends through the marked stool 84 and agroup A which extends through the air 88 within the colon 66. The pixelsof the polyp group P have intensity values in the range of 50 HU. Thepixels of the marked stool group S have intensity values in the range of900 HU. The pixels of the air group A have intensity values in the rangeof −900 HU.

The digital image processing methods used to perform marked stoolidentification step 56 (FIG. 2) during the tests of the inventiondescribed below generally include the three steps illustrated in FIG.5: 1) marked stool perimeter identification step 70; 2) island removalstep 72; and 3) perimeter edge expansion step 74. The marked stoolperimeter identification step 70 is performed by a thresholdingoperation. The thresholding operation makes use of a marked stoolthreshold value which is selected as the minimum pixel intensity valuerepresentative of marked stool. The marked stool threshold value can beselected to optimize the identification of marked stool on the basis ofa variety of factors including the type of stool marker used, thequality of the stool marking procedure on a given patient and imagingparameters. A marked stool threshold value of 150 HU was used during thetests of the invention described below. Pixels having intensity valuesgreater than 150 HU are designated as those representing marked stool inthe image, while pixels having intensity values less than or equal to150 HU are designated as representing other features of the image (e.g.,air 88, unmarked stool 86 and the colon wall 80).

During the marked stool perimeter identification step 70, the pixelintensity values of the image are compared to the marked stool thresholdvalue to determine whether they represent marked stool 84 or other imagefeatures such as colon wall 80. The result of this thresholdingoperation is data representing a map of areas of the imagerepresentative of marked stool 84. The locations of the edges orperimeters of the areas of marked stool 84 can then be identified. Inthe image shown in FIG. 6, for example, the outer perimeter 92 of themarked stool 84 can be identified, as well as the inner perimeter 94 ofthe volume of unmarked stool 86 within the marked stool.

During the island removal step 72, all features of the image such as theunmarked stool 86 which have been identified as representing somethingother than marked stool 84, and which are completely surrounded by themarked stool (i.e., are within the perimeter 92), are “removed” from theimage. This removal operation is performed because the completelysurrounded volume is presumed to represent features of the image otherthan the colon wall 80 or polyp 82. In the image shown in FIG. 6, thepolyp 82 would not be removed from the image since it is attached to thecolon wall 80 and not completely surrounded by the marked stool 84. Inone embodiment of the invention, island features such as unmarked stool86 which are removed from the image are replaced with pixel valuesrepresenting marked stool. FIG. 8 is an illustration of the imagecorresponding to that in FIG. 6 after the island of unmarked stool 86has been removed and replaced with pixel intensity values correspondingto the marked stool 84.

As shown in FIGS. 6 and 7, the intensity values of the pixels at theperimeter 92 of the marked stool 84 do not shift immediately betweenvalues representative of marked stool and those representative of otherfeatures such as air 88. Instead, there is an edge transition distanceat the perimeter 92 over which the range of pixel intensity valueschange. The edge transition distance is due to a number of factorsincluding the relatively low quantity of marked stool 84 at theperimeter 92. It has been observed that the perimeters 92 identifiedduring the step 70 described above (i.e., the initially identifiedperimeter) can sometimes be insufficient to represent the actualperimeter of the identified area of marked stool 84.

Perimeter edge expansion step 74 is performed to effectively sharpen theedge and enhance the accuracy of the identification of the initiallyidentified perimeter 92 of marked stool 84. Briefly, the edge expansionstep 74 determines whether the perimeter 92 is adjacent to the air 88within the colon 66, or adjacent to soft tissues such as wall 80 orpolyp 82. The identified perimeter 92 of the marked stool is thenconditionally expanded based on the determination. If it is determinedthat the perimeter 92 is adjacent to air 88 within the colon 66, theidentified perimeter is expanded to include pixels having intensityvalues less than the marked stool threshold value on the basis that theyrepresent unmarked stool rather than other features such as the colonwall 80 or polyp 82. Conversely, if it is determined that the perimeter92 is adjacent to walls 80 or polyp 82, the identified perimeter is notexpanded on the basis that the pixels adjacent to the initiallyidentified perimeter represent the colon walls or polyps rather thanunmarked stool.

The edge expansion step 74 makes use of an expansion distance thresholdvalue and an air intensity threshold value. The expansion distancethreshold is a distance, in terms of number of pixels, beyond theinitially identified perimeter 92 which is evaluated to identify otherfeatures such as air 88, colon walls 80 and polyps 82 adjacent to theperimeter. In the tests of the invention described below, the expansiondistance threshold was set at a number of pixels which correspondsgenerally to a distance of 2-3 mm. Other values can be used for theexpansion distance threshold to optimize the edge expansion step 74 forparticular applications and algorithms.

The air intensity threshold value is a pixel intensity value, in HU,which is selected as the maximum pixel intensity value representative ofair 88 within the colon 66. The air intensity threshold value can beselected to optimize the identification of air 88 from other featuressuch as unmarked stool on the basis of a variety of factors includingthe type of stool marker used, the quality of the stool markingprocedure on a given patient and imaging parameters. An air intensitythreshold value of −500 HU was used during the tests of the inventiondescribed below. Pixels having intensity values less than −500 HU aredesignated as those representing air in the image, while pixels havingintensity values greater than or equal to −500 HU are designated asrepresenting other features of the image (e.g., unmarked stool and thecolon wall 80).

FIG. 9 is a flowchart which generally describes the digital imageprocessing methods which can be used to perform the edge expansion step74. As shown, the intensity values of the pixels within the expansiondistance threshold and beyond the initially identified perimeter 92 arecompared to the air intensity threshold value at step 100. If it isdetermined that the pixel intensity values within the expansion distancethreshold are greater than or equal to the air intensity threshold valueat step 102, the initially identified perimeter 92 is not expanded asindicated by step 104. This sequence of steps 100, 102 and 104 can beillustrated with reference to FIGS. 6 and 7. In these Figures the pixelsof stool group S all have intensity values greater than 150 HU. Thepixels of the polyp group P that are within the expansion distancethreshold D of the stool group S all have intensity values which aregreater than an air intensity threshold value of −500 HU. Accordingly,the initially identified perimeter 92 of the marked stool 84 is notexpanded at the interface between the pixels of the polyp group P andstool group S in the row 90.

If it is determined that pixel intensity values within the expansiondistance threshold are less than the air intensity threshold value atstep 102, the initially identified perimeter 92 is expanded as indicatedat step 106. In the embodiment described in FIG. 9, the distance of theexpansion is equal to the number of pixels within the expansion distancethreshold that have intensity values greater than the air thresholdvalue. This sequence of steps 100, 102 and 106 is also illustrated inFIGS. 6 and 7. In these Figures the pixels of the air group A that arewithin the expansion distance threshold D of the stool group S includepixels which are less than the air intensity threshold value of −500 HU.Accordingly, the initially identified perimeter 92 of the marked stool84 is enlarged to include the pixels of expanded stool group S_(E)(i.e., those pixels within the expansion distance threshold D which haveintensity values greater than −500 HU.

Other edge expansion algorithms can also be used. In another embodimentof the invention, for example, the initially identified perimeter 92 isexpanded to include all pixels within the expansion distance thresholdwhich have intensity values greater than the air intensity thresholdvalue. Recursive image processing methodologies can be used to implementthis and other edge expansion algorithms.

With reference back to FIG. 2, following the completion of marked stoolidentification step 56, the images are processed to remove theidentified marked stool 84 within the edge expanded perimeter 92 asshown in FIG. 6. In one embodiment of the invention, the marked stool 84is replaced with pixel intensity values representing air. The markedstool can also be replaced with other image features in accordance withthe preferences of the radiologist that will be performing diagnosesusing the images. For example, when processed in three-dimensional form,the identified stool can be replaced with the colon wall 80, polyps orother features that may be present in the field of view behind themarked and removed stool 84.

FIG. 10 is an illustration of the image corresponding to that in FIG. 8after the marked stool 84 has been removed and replaced with pixelintensity values corresponding to air 88. For purposes of comparison,FIG. 11 is an illustration of an image corresponding to that in FIG. 8in which the stool 84 has not been marked. As shown in FIG. 11, it canbe difficult to visually distinguish the unmarked stool 84 from thepolyp 82 since they have similar densities in the image. Residual stool84 in the colon 66 can therefore mask the presence of polyps 82,reducing the efficacy of colorectal screening procedures. After thestool 84 has been virtually removed from the image, polyps such as 82that might have been masked are generally more readily identified.

Image processing techniques for implementing the stool identificationand removal steps 56 and 58, respectively, described above, aregenerally known. Any conventional or otherwise known techniques forperforming the functions of the described steps 56 and 58 can be used toimplement the invention. Also, although the tests described below wereperformed using images processed in two-dimensional form, the steps 56and 58 can be implemented in three-dimensional form as well usingsimilar image processing techniques. Use of the invention inthree-dimensional form can also offer enhanced efficacy. For example,the feature identified as the island of unmarked stool 86 (FIG. 6) usingthe two-dimensional processing form described above could be the end ofa polyp which is connected to the colon wall. Application of theinvention in three-dimensional form could identify such a feature as apolyp under these circumstances since it would not meet the removalcriterion of step 72 (i.e., is not completely surrounded by markedstool).

After the set colonography images are generated in the manner describedabove, they are displayed to a radiologist for diagnosis as shown bystep 60 in FIG. 2. The colonography images can be displayed to theradiologist in any conventional or otherwise known manner preferred bythe radiologist. By way of example, a variety of image displayapproaches that can be used for this purpose are described in the patentdocuments referenced in the Background of the Invention section above.FIG. 22A is a two-dimensional CT image of portion of a colon whichincludes a section of stool marked in accordance with the methoddescribed above. FIG. 22B is a two-dimensional CT image of the sameportion of the colon shown in FIG. 22A, from which the section of markedstool has been removed in accordance with the method described above.FIG. 23A is a three-dimensional CT image of portion of a colon whichincludes a section of stool marked in accordance with the presentinvention.

FIG. 23B is a three-dimensional CT image of the same portion of thecolon shown in FIG. 23A, from which the section of marked stool has beenremoved in accordance with the present invention.

A comprehensive test of the invention was performed on a study grouppopulation including 32 male and 25 female patients, all of whom wereknown or suspected to have colorectal polyps or colon cancer. Thereferral sources were conventional barium enema exams, flexiblesigmoidoscopy exams and colorectal surgery. The study population wasdivided into 5 groups. The study protocol called for the patients ofeach group to be administered 225 ml (7.5 oz) doses of suspended bariumsulfate solution over a range of time schedules. The barium sulfatesolution was obtained from Medefield Pty Ltd of Artarmon NSW, Australia.The barium sulfate solution was similar to the company's MedeScan bariumoral contrast solutions, with the amount of barium reduced to 1.2% andreduced levels of suspension agents. This barium sulfate solution wasfound to produce reduced levels of streaks and artifacts in the image,as well as minimizing coating of the colon.

FIG. 12 is a chart describing the barium sulfate administration schedulefor of the 5 groups, and the number of patients (No. pts) in each group.As shown, the period of administration ranged from 24 to 48 hours priorto imaging, while the total number of doses administered ranged from 2to 7. FIG. 13 is a detailed description of the timing of theadministration for the two groups of patients that received the dosesover a 24 hour period. FIG. 14 is a detailed description of the timingof the administration for the three groups of patients that received thedoses over a 48 hour period.

As noted above, the imaging for the test was performed on a commerciallyavailable General Electric Light Speed model CT scanner. The imager wasconfigured for multislice operation at 50 mA, 5 mm slice thickness, 3 mmreconstruction intervals, HQ mode and 15 mm/rotation table speed. Thecolons of all patients were insufflated with air. Images were taken withthe patients in both the prone and supine images. The images werepresented to the radiologists in the formats described in PCTpublication WO 98/32371. No cathartics were administered to the patientprior to the imaging.

With the marked stool threshold value set to 150 HU, the colonographyimages from each patient of each group were assigned a score between 1and 4 to describe the extent or degree by which the associated bariumsulfate suspension administration protocol was effective at labeling ormarking stool present within the colons of the associated patients. FIG.15 is an illustration of the scoring system, with the listed percentagerange being the amount of stool in the colons that was adequately markedby the associated protocol. Individual scores were assigned for eachsection (cecum, right, transverse, left, sigmoid and rectum) of thecolon.

FIG. 16 is a CT image of a cross section of an abdomen includingportions of a colon, and a detailed CT image of a portion of the colon,illustrating an example of the type of stool marking that would beassigned a score of 0 in the test. FIG. 17 is a CT image of a crosssection of an abdomen including portions of a colon, and a detailed CTimage of a portion of the colon, illustrating an example of the type ofstool marking that would be assigned a score of 1 in the test. FIG. 18is a CT image of a cross section of an abdomen including portions of acolon, and a detailed CT image of a portion of the colon, illustratingan example of the type of stool marking that would be assigned a scoreof 2 in the test. FIG. 19 is a CT image of a cross section of an abdomenincluding portions of a colon, and a detailed CT image of a portion ofthe colon, illustrating an example of the type of stool marking thatwould be assigned a score of 3 in the test. FIG. 20 is a CT image of across section of an abdomen including portions of a colon, and adetailed CT image of a portion of the colon, illustrating an example ofthe type of stool marking that would be assigned a score of 4 in thetest.

FIG. 21 is a graph of the stool labeling efficacy obtained from the twogroups of patients administered doses of barium sulfate suspension overa 24 hour period. A separate score is provided for each of the sectionsof the colon. FIG. 22 is a graph of the stool labeling efficacy obtainedfrom the three groups of patients administered doses of barium sulfatesuspension over a 48 hour period. Again, a separate score is providedfor each of the sections of the colon. From the test results illustratedin FIGS. 21 and 22 it is evident that orally administered barium sulfatesuspensions are capable of mixing with stool throughout the colon to alevel which is sufficient to enable the stool to be identified and bothvisually and electronically discriminated from other colon tissues. Itappears from this test data that the quality of the stool marking (i.e.,the test scores) is more closely related to the quantity of the stoolmarker administered to the patient than to the length of time over whichthe marker was administered. It also appears that the administration ofstool marker at times relatively close to the imaging procedure (e.g.,within 6 hours of the exam) also enhanced the quality of the stoolmarking.

FIG. 22 is a chart describing the percent of polyps that were detectedon the basis of a review of the colonography images for each of thestudy groups. The percentage of detection was especially high in thestudy groups that were administered the barium sulfate suspension over48 hour periods. On the basis of these tests it is evident that thedetection of polyps less than or equal to 1 cm is possible with arelatively high degree of sensitivity. This sensitivity is similar tothat reported using conventional colonography techniques on a fullyprepared colon.

Another test similar to that described above was conducted usingpowdered or flaked barium administered to the patients in pill (capsule)form. One group of patients in this test received capsules filled with600 mg of commercially available Barosperse. Another group of patientsin the test received capsules filled with 600 mg of commerciallyavailable USP barium. Both groups of patients were administered 3 pillswith all three meals and at bedtime during the two days preceding theimaging procedure and three pills the morning of the imaging procedure(i.e., a total of twenty seven 600 mg pills). An 8 oz dose of 2.0%liquid barium suspension was also administered orally 30-60 minutesprior to the imaging procedure. The results of the test in terms ofstool labeling scoring and percentage of polyp detection for both groupsof patients was similar to the results obtained with the group ofpatients that were administered 7 doses of barium sulfate suspensionover the 48 hour period before the imaging procedure.

The virtual colon preparation and colonography technique of the presentinvention offers important advantages. In particular, it is veryconvenient and efficient to implement, and will therefore result inenhanced patient acceptance and compliance. Furthermore, the methodologyis capable of producing highly efficacious diagnoses.

Although the present invention has been described with reference topreferred embodiments, those skilled in the art will recognize thatchanges can be made in form and detail without departing from the spiritand scope of the invention. In particular, although it can beadvantageous to simulate colon cleansing by electronically removing themarked stool, efficacious colorectal cancer screening diagnoses can alsobe made through visual observations of the colonography images with themarked stool present. This is especially the case when the stool isthoroughly marked, and the visual characteristics of the marked stoolare clearly distinguishable from those of the soft tissues. Also, otherimage processing techniques can be used to identify the marked stoolwithin the colon. Furthermore, although the present invention can beused in connection with an unprepared colon, it can also enhance theefficacy of colonography diagnostic procedures performed on patientsthat have followed conventional preparation processes to varyingdegrees. In general, the less stool in the colonography images, even ifmarked in accordance with this invention, the less the likelihood thatpolyps or other tissues of interest to a radiologist will be masked bythe stool.

1. A method for imaging a patient's unprepared colon for colorectalpolyp screening, comprising: prescribing the administration of a stoolmarker protocol enabling marked stool to be discriminated from polypshaving a diameter of at least 1 cm when imaged, wherein the protocolincludes administering at least about 10 grams of stool marker in atleast six doses to the patient over at least a 48 hour administrationperiod; and with the patient free from colon preparation, including fromthe administration of laxatives or cathartics for at least 24 hours,imaging the patient's colon after the administration period to generateimage data representative of a sequence of image slices along a lengthof the colon, the imaging being performed by an imaging modality capableof generating image slice data with slice thicknesses no greater than 5mm and reconstruction intervals no greater than 3 mm enabling thediscrimination of polyps having a diameter of at least 1 cm from markedstool in the image slices.
 2. The method of claim 1 and furtherincluding displaying the images.
 3. The method of claim 1 whereinprescribing the administration of stool marker includes prescribing theadministration of a pill including stool marker.
 4. The method of claim1 wherein prescribing the administration of doses of barium stool markerincludes prescribing the administration of doses of barium sulfatesuspension including between about 0.8% and 1.5% barium.
 5. The methodof claim 1 and further including producing and displaying images of thepatient's colon.